The present invention relates generally to waveguide illumination system and, more particularly, to waveguide illumination assembly for an automotive license plate.
Vehicle license plates must be illuminated at a prescribed intensity in accordance with the Federal Motor Vehicle Safety Standard, FMVSS 108 guidelines as well as other international regulations such as ECE Regulation 4. The FMVSS 108 regulatory test consists of eight illumination measurement sites spaced across the entire face of the license plate. In order to meet the regulatory illumination requirements light must be distributed evenly across the entire license plate face from a source located outward of the license plate perimeter. Illumination of a license plate directly from a single light bulb is likely to produce hot spots, wherein areas of the plate are over illuminated and other areas are not illuminated enough. Consequently, in order to distribute light evenly across the license plate, thereby avoiding hot spots of concentrated light, a multitude of light bulbs are typically utilized for illumination. This type of design can be expensive to manufacture and replacement of the bulbs is a maintenance concern for the customer.
U.S. Pat. No. 2,689,948 granted to Gerald S. Rothman, Sep. 21, 1954, discloses a form of waveguide utilized in connection with a vehicle license plate. However, the Rothman waveguide is for aesthetic and signaling purposes and not for illumination of a license plate. Furthermore, the Rothman patent teaches that a waveguide can glow or appear illuminated with the incorporation of evenly spaced and identical notches placed into the glowing surface. The glow is a result of internal light rays being reflected externally out of the waveguide.
The notches, however, are not used for illumination of the license plate; rather, they direct the light in the waveguide outward away from the license plate. Also, because the notches are placed upon the outer aesthetic surface portion of the waveguide, they can collect dirt which will block the aesthetic illumination from the waveguide. This illumination degradation is compounded by the decreasing concentration of internal light rays available for external reflection through each succeeding notch. With each notch being the same size and spaced evenly apart, the end of the waveguide positioned closest to the light source will glow brighter than the tail end. Therefore, even light distribution is not achieved.
In accordance with the present invention, there is provided a waveguide illumination assembly positioned outward from the perimeter of a license plate. The waveguide illumination assembly includes a single light source which emits light rays into a coupling end of a transport. Congruently attached to a tail end of the transport is at least one arm. Each arm receives a proportionate intensity of light from the transport. The arms each have an outboard side, an inboard side and a termination end. The inboard side is configured longitudinally between the outboard side and the license plate. The outboard side has an array of reflective elements for internally reflecting light rays at prescribed angles causing the same light rays to refract through the inboard side and onto the license plate.
These elements vary progressively in the forward direction accounting for the changing concentrations of light rays within the light transport.
To enhance the efficiency of the waveguide, a reflective coating or shell is preferably positioned over the outboard side of each arm to reflect any escaping light rays back into the waveguide. Although not of primary importance, this coating may also keep the outboard side free of dirt and scratches which could degrade the internal reflective characteristics of the outboard side. The inboard side is preferably polished smooth creating a surface least likely to collect dirt and easy to clean.
Another variation of the array of reflective elements preferably includes an outboard side with a roughened surface. The roughness of the roughened surface progressively increases in the forward direction thereby adjusting for the decreasing concentration of internal light rays by increasing the internal reflection characteristics of the outboard side capable of causing refraction through the inboard side. This variation of roughness assures an even light distribution across the license plate thereby meeting FMVSS 108 regulatory requirements.
An advantage of the present invention is the use of a single light source, thereby minimizing maintenance costs.
Another advantage of the present invention is that it provides an even distribution of light across the license plate.